I don't know where the samples come from. This is just a guess, but I would take a wild shot and say that the samples come from some old Roland drum machine of some sort and he distorted them. I don't actually know though. If there was an Aphex Twin Sound Sources Sheet (God I wish there was) I could confirm it. But no, there's not a sheet of that out there. I think...
Have you ever wanted to make a Wii Music cover like AdamCrossing? But you just can't hack Wii Music, even using Wii Music Editor? Well I have the perfect solution! Introducing...the Wii Music (Instruments) Soundfont! With this, you can make your own Wii Music Covers without having to hack the game! It's ripped from the game's files so it's not some crappy fan-made one! Anyway, Have Fun! Thanks,